In a package having a structure in which insulating layers (e.g., resin layers) are formed respectively on top and bottom sides of an inner wiring layer, and in which interlayer connection vias are formed in the resin layers, lands (or pads) each required for ensuring conduction with the vias are arranged in the inner wiring layer. The size of each of the lands is designed, regardless of the cross-sectional shape of the land, on the basis of a value calculated in consideration of the size of a via to be connected thereto, variations in formation position of the via, variations in formation position of the land and the like.
In addition, where a laser is used to form the vias, the processing output (laser output), or the number of shots needs to be changed for changing the diameter of the laser via. Further, a resin residue (smear) remains in the via hole opened by the laser processing. Thus, uniformity may be decreased in desmearing to remove the resin residue or in plating to be performed thereafter. For this reason, it has been a general practice in the conventional art to use vias having the same diameter at least for the same wiring layer and then to use the lands with the same size.
As an example of the technique related to the conventional art, there is a multilayer wiring board described in Patent document 1 (Japanese Laid-open Patent Publication No. 2005-72328). As another technique, there is a multilayer wiring board described in Patent document 2 (Japanese Laid-open Patent Publication No. 2003-158379).
The size of a land as described above is preferably made as large as possible for the purpose of ensuring connection reliability with the via. On the other side, for the purpose of increasing the wiring density, the size of the land needs to be made as small as possible so that the increased portion of the wiring layer can be used as a region used to form a normal wiring pattern.
Where a wiring is formed by subtractive method, a slope in accordance with the thickness of the wiring is formed on the side surface of the wiring (side surface of the land) during etching. Namely, the land is formed in a tapered shape. Accordingly, there occurs a difference in size between the upper surface and the lower surface of the land.
Where vias are formed on an inner wiring layer in directions toward both surfaces of the wiring layer, respectively, the land sizes required respectively for the upper and lower surfaces of the wiring may be the same if the land is used for vias with the same diameter. However, where the lands are uniformly designed with the same size regardless of the directions in which the corresponding vias are connected, there occurs a problem. Specifically, for the purpose of ensuring the connection reliability, the smaller one of the lower and upper surface sizes needs to be set as the lower limit of the sizes. As a result, there occurs a problem in that the size of the opposite side surface of the land becomes excessively (unnecessarily) large.
Where a land is provided in an unnecessarily large size, the region of the wiring layer that can be used as the region used to form a wiring pattern is reduced by the unnecessary amount of the land. This leads to a decrease in the wiring density. Moreover, the decrease in the region usable for wiring may lead to a need to set finer wiring rules, or to increase the number of wiring layers, thus causing a difficulty in manufacturing.